Tests if the specified bit is set.
n can be any integer from [0,7]. It must be defined on compile time.
bit n,a bit n,b bit n,c bit n,d bit n,e bit n,h bit n,l bit n,(hl) bit n,(ix+n) bit n,(iy+n)
Opposite of the nth bit is written into the Z flag. C is preserved, N is reset, H is set, and S and P/V are undefined.
ld a,%00000001 bit 0,a ;would reset Z bit 1,a ;would set Z
r denotes 8-bit register.